The safe treatment and disposal of all waste materials is demanded in most developed nations. In this regard, there is a growing demand on industry by environmentalists and government agencies to alleviate potentially toxic and/or contaminated waste disposal sites that were employed for many years prior to the public's heightened environmental concerns and the enactment of environmental legislation.
For example, a number of now defunct lead-acid battery recycling sites were operated where lead was reclaimed from spent lead-acid batteries. At most such lead-acid battery recycling sites, the primary operation consisted of breaking the battery case, draining the spent acid, and separating the battery cases from the commercially valuable lead to be recycled. The broken battery cases, which were at that time formed of a non-recyclable, hardened rubber material known in art parlance as "ebonite", were of no commercial value and were thus typically discarded as landfill waste. However, it is now known that these discarded battery cases in landfills nonetheless were contaminated with sufficient quantities of lead that could detrimentally affect the environment.
Various techniques have been proposed for the remediation of landfills containing lead-contaminated waste lead-acid battery casings. For example, The U.S. Bureau of Mines has proposed a chemical reclamation process for waste lead-acid battery casings whereby battery casing particles are carbonized by treatment in a sodium or ammonium carbonate solution followed by acid washing with nitric acetic or flurosilicic acids. See, "The Hazardous Waste Consultant", September/October 1991, pages 1.22-1.24.
Simply immobilizing the lead contamination at landfills has been identified as one possible option recently by Royer et al, "Control Technologies for Remediation of Contaminated Soil and Waste Deposits at Superfund Lead Battery Recycling Sites", Journal of Air & Waste Management Association, Volume 42, No. 7, pgs. 970-980 (July 1992). However, the authors indicate that immobilization by vitrification would be unsuitable due to the combustible nature of the casings.
It would therefore undoubtedly be desirable for a process to be proposed whereby landfill materials containing both lead-contaminated soil and waste lead-acid battery casings could be treated so as to ameliorate the environmental concerns posed by such landfill materials. It is towards providing such a process that the present invention is directed.
Broadly, the present invention is especially characterized in the treatment of lead-contaminated soil and battery casings using a plasma arc furnace which pyrolyzes the soil and waste battery casings so as to form a vitrified slag and a combustible gas, respectively. The combustible gas (which contains predominantly carbon monoxide) along with volatilized heavy metals (of which lead predominates) is directed to, and used as, a primary fuel by a conventional lead smelting furnace. The volatilized lead that is entrained in the combustible gas is thus transferred thereby to the lead recovery and environmental protection/control equipment associated with the smelting furnace. The soil, on the other hand, is converted into a non-toxic (i.e., according to the Toxicity Characteristic Leaching Procedure (TCLP) published in the Federal Register on Mar. 29, 1989, the entire content of which is expressly incorporated hereinto by reference) vitrified slag by the plasma arc which may be crushed and used as a commercial material (e.g., roadway aggregate, asphalt filler material or the like) or simply transferred to a landfill where it poses no environmental threat.
Further aspects and advantages of this invention will become apparent after careful consideration is given to the following detailed description of the preferred exemplary embodiment thereof.